21 files declare their use of DateFormat

comment.tokens.inc in core/modules/comment/comment.tokens.inc
Builds placeholder replacement tokens for comment-related data.
CommentActionsTest.php in core/modules/comment/tests/src/Kernel/CommentActionsTest.php
CommentOrphanTest.php in core/modules/comment/tests/src/Kernel/CommentOrphanTest.php
DateFormatAccessControlHandlerTest.php in core/modules/system/tests/src/Kernel/DateFormatAccessControlHandlerTest.php
DateFormatResourceTestBase.php in core/tests/Drupal/FunctionalTests/Rest/DateFormatResourceTestBase.php
DateFormatTest.php in core/modules/jsonapi/tests/src/Functional/DateFormatTest.php
DateFormatTest.php in core/modules/system/tests/src/FunctionalJavascript/System/DateFormatTest.php
DateRangeFieldTest.php in core/modules/datetime_range/tests/src/Functional/DateRangeFieldTest.php
Datetime.php in core/lib/Drupal/Core/Datetime/Element/Datetime.php
DateTimeFieldTest.php in core/modules/datetime/tests/src/Functional/DateTimeFieldTest.php
DateTimeTest.php in core/modules/system/tests/src/Functional/System/DateTimeTest.php
file.module in core/modules/file/file.module
Defines a "managed_file" Form API field and a "file" field for Field module.
MigrateDateFormatTest.php in core/modules/system/tests/src/Kernel/Migrate/d6/MigrateDateFormatTest.php
node.tokens.inc in core/modules/node/node.tokens.inc
Builds placeholder replacement tokens for node-related data.
SummaryLengthTest.php in core/modules/node/tests/src/Kernel/SummaryLengthTest.php
system.tokens.inc in core/modules/system/system.tokens.inc
Builds placeholder replacement tokens system-wide data.
TimestampDatetimeWidget.php in core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
TimestampTest.php in core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
TimezoneTest.php in core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php
user.tokens.inc in core/modules/user/user.tokens.inc
Builds placeholder replacement tokens for user-related data.
UserTimeZoneTest.php in core/modules/user/tests/src/Functional/UserTimeZoneTest.php

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